Package 'jointCalib'

Title: A Joint Calibration of Totals and Quantiles
Description: A small package containing functions to perform a joint calibration of totals and quantiles. The calibration for totals is based on Deville and Särndal (1992) <doi:10.1080/01621459.1992.10475217>, the calibration for quantiles is based on Harms and Duchesne (2006) <https://www150.statcan.gc.ca/n1/en/catalogue/12-001-X20060019255>. The package uses standard calibration via the 'survey', 'sampling' or 'laeken' packages. In addition, entropy balancing via the 'ebal' package and empirical likelihood based on codes from Wu (2005) <https://www150.statcan.gc.ca/n1/pub/12-001-x/2005002/article/9051-eng.pdf> can be used. See the paper by Beręsewicz and Szymkowiak (2023) for details <arXiv:2308.13281>. The package also includes functions to reweight the control group to the treatment reference distribution and to balance the covariate distribution using the covariate balancing propensity score via the 'CBPS' package for binary treatment observational studies.
Authors: Maciej Beręsewicz [aut, cre]
Maintainer: Maciej Beręsewicz <[email protected]>
License: GPL-3
Version: 0.1.2
Built: 2024-11-04 04:18:57 UTC
Source: https://github.com/ncn-foreigners/jointcalib

Help Index


An internal function for calibration of weights using empirical likelihood method

Description

calib_el performs calibration using empirical likelihood (EL) method. The function is taken from Wu (2005). If algorithm has problem with convergence constrOptim is used instead (as in Zhang, Han and Wu (2022)).

In (pseudo) EL the following (pseudo) EL function is maximized

\[\sum_{i \in r} d_i\log(p_i),\]

under the following constraint

\[\sum_{i \in r} p_i = 1,\]

with constraints on quantiles (with notation as in Harms and Duchesne (2006))

\[\sum_{i \in r} p_i(a_{i} - \alpha/N) = 0,\]

where \(a_{i}\) is created using joint_calib_create_matrix function, and possibly means

\[\sum_{i \in r} p_i(x_{i} - \mu_{x}) = 0,\]

where \(\mu_{x}\) is known population mean of X. For simplicity of notation we assume only one quantile and one mean is known. This can be generalized to multiple quantiles and means.

Usage

calib_el(
  X,
  d,
  totals,
  maxit = 50,
  tol = 1e-08,
  eps = .Machine$double.eps,
  att = FALSE,
  ...
)

Arguments

X

matrix of variables for calibration of quantiles and totals (first column should be intercept),

d

initial d-weights for calibration (e.g. design-weights),

totals

vector of totals (where 1 element is the population size),

maxit

a numeric value giving the maximum number of iterations,

tol

the desired accuracy for the iterative procedure,

eps

the desired accuracy for computing the Moore-Penrose generalized inverse (see MASS::ginv()),

att

indicating whether the weights should sum up treatment group (for joint_calib_att function),

...

arguments passed to stats::optim via stats::constrOptim.

Value

Returns a vector of empirical likelihood g-weights

Author(s)

Maciej Beręsewicz based on Wu (2005) and Zhang, Han and Wu (2022)

References

Wu, C. (2005). Algorithms and R codes for the pseudo empirical likelihood method in survey sampling. Survey Methodology, 31(2), 239 (code is taken from https://sas.uwaterloo.ca/~cbwu/Rcodes/LagrangeM2.txt).

Zhang, S., Han, P., and Wu, C. (2023) Calibration Techniques Encompassing Survey Sampling, Missing Data Analysis and Causal Inference. International Statistical Review, 91: 165–192. https://doi.org/10.1111/insr.12518 (code is taken from Supplementary Materials).

Examples

## generate data based on Haziza and Lesage (2016)
set.seed(123)
N <- 1000
x <- runif(N, 0, 80)
y <- exp(-0.1 + 0.1*x) + rnorm(N, 0, 300)
p <- rbinom(N, 1, prob = exp(-0.2 - 0.014*x))
totals_known <- c(N=N, x=sum(x))
df <- data.frame(x, y, p)
df_resp <- df[df$p == 1, ]
df_resp$d <- N/nrow(df_resp)
res <- calib_el(X = model.matrix(~x, df_resp),
                d = df_resp$d,
                totals = totals_known)
data.frame(known = totals_known, estimated=colSums(res*df_resp$d*model.matrix(~x, df_resp)))

control parameters

Description

control_calib is function that contains control parameters for joint_calib_create_matrix

Usage

control_calib(
  interpolation = c("logit", "linear"),
  logit_const = -1000,
  sum_to_sample = FALSE,
  sum_to_one = FALSE,
  survey_sparse = FALSE,
  ebal_constraint_tolerance = 1,
  ebal_print_level = 0,
  el_att = FALSE
)

Arguments

interpolation

type of interpolation: logit or linear,

logit_const

constant for logit interpolation,

sum_to_sample

whether weights should sum to sample,

sum_to_one

whether weights should sum to one (aka normalized weights),

survey_sparse

whether to use sparse matrices via Matrix package in survey::grake() (currently not supported),

ebal_constraint_tolerance

this is the tolerance level used by ebalance to decide if the moments in the reweighted data are equal to the target moments (see ebal::ebalance()),

ebal_print_level

controls the level of printing: 0 (normal printing), 2 (detailed), and 3 (very detailed) (see ebal::ebalance()),

el_att

whether weights for control should sum up to treatment size (for calib_el function only).

Value

a list with parameters

Author(s)

Maciej Beręsewicz


Function for the joint calibration of totals and quantiles

Description

joint_calib allows joint calibration of totals and quantiles. It provides a user-friendly interface that includes the specification of variables in formula notation, a vector of population totals, a list of quantiles, and a variety of backends and methods.

Usage

joint_calib(
  formula_totals = NULL,
  formula_quantiles = NULL,
  data = NULL,
  dweights = NULL,
  N = NULL,
  pop_totals = NULL,
  pop_quantiles = NULL,
  subset = NULL,
  backend = c("sampling", "laeken", "survey", "ebal", "base"),
  method = c("raking", "linear", "logit", "sinh", "truncated", "el", "eb"),
  bounds = c(0, 10),
  maxit = 50,
  tol = 1e-08,
  eps = .Machine$double.eps,
  control = control_calib(),
  ...
)

Arguments

formula_totals

a formula with variables to calibrate the totals,

formula_quantiles

a formula with variables for quantile calibration,

data

a data.frame with variables,

dweights

initial d-weights for calibration (e.g. design weights),

N

population size for calibration of quantiles,

pop_totals

a named vector of population totals for formula_totals. Should be provided exactly as in survey package (see survey::calibrate),

pop_quantiles

a named list of population quantiles for formula_quantiles or an newsvyquantile class object (from survey::svyquantile function),

subset

a formula for subset of data,

backend

specify an R package to perform the calibration. Only sampling, laeken, survey, ebal or base are allowed,

method

specify method (i.e. distance function) for the calibration. Only raking, linear, logit, sinh, truncated, el (empirical likelihood), eb (entropy balancing) are allowed,

bounds

a numeric vector of length two giving bounds for the g-weights,

maxit

a numeric value representing the maximum number of iterations,

tol

the desired accuracy for the iterative procedure (for sampling, laeken, ebal, el) or tolerance in matching population total for survey::grake (see help for survey::grake)

eps

the desired accuracy for computing the Moore-Penrose generalized inverse (see MASS::ginv())

control

a list of control parameters (currently only for joint_calib_create_matrix)

...

arguments passed either to sampling::calib, laeken::calibWeights, survey::calibrate or optim::constrOptim

Details

Imports for the function

Value

Returns a list with containing:

  • g – g-weight that sums up to sample size,

  • Xs – matrix used for calibration (i.e. Intercept, X and X_q transformed for calibration of quantiles),

  • totals – a vector of totals (i.e. N, pop_totals and pop_quantiles),

  • method – selected method,

  • backend – selected backend.

Author(s)

Maciej Beręsewicz

References

Beręsewicz, M., and Szymkowiak, M. (2023). A note on joint calibration estimators for totals and quantiles Arxiv preprint https://arxiv.org/abs/2308.13281

Deville, J. C., and Särndal, C. E. (1992). Calibration estimators in survey sampling. Journal of the American statistical Association, 87(418), 376-382.

Harms, T. and Duchesne, P. (2006). On calibration estimation for quantiles. Survey Methodology, 32(1), 37.

Wu, C. (2005) Algorithms and R codes for the pseudo empirical likelihood method in survey sampling, Survey Methodology, 31(2), 239.

Zhang, S., Han, P., and Wu, C. (2023) Calibration Techniques Encompassing Survey Sampling, Missing Data Analysis and Causal Inference, International Statistical Review 91, 165–192.

Haziza, D., and Lesage, É. (2016). A discussion of weighting procedures for unit nonresponse. Journal of Official Statistics, 32(1), 129-145.

See Also

sampling::calib() – for standard calibration.

laeken::calibWeights() – for standard calibration.

survey::calibrate() – for standard and more advanced calibration.

ebal::ebalance() – for standard entropy balancing.

Examples

## generate data based on Haziza and Lesage (2016)
set.seed(123)
N <- 1000
x <- runif(N, 0, 80)
y <- exp(-0.1 + 0.1*x) + rnorm(N, 0, 300)
p <- rbinom(N, 1, prob = exp(-0.2 - 0.014*x))
probs <- seq(0.1, 0.9, 0.1)
quants_known <- list(x=quantile(x, probs))
totals_known <- c(x=sum(x))
df <- data.frame(x, y, p)
df_resp <- df[df$p == 1, ]
df_resp$d <- N/nrow(df_resp)
y_quant_true <- quantile(y, probs)
## standard calibration for comparison
result0 <- sampling::calib(Xs = cbind(1, df_resp$x),
                           d = df_resp$d,
                           total = c(N, totals_known),
                           method = "linear")

y_quant_hat0 <- laeken::weightedQuantile(x = df_resp$y,
                                         probs = probs,
                                         weights = result0*df_resp$d)
x_quant_hat0 <- laeken::weightedQuantile(x = df_resp$x,
                                         probs = probs,
                                         weights = result0*df_resp$d)

## example 1: calibrate only quantiles (deciles)
result1 <- joint_calib(formula_quantiles = ~x,
                       data = df_resp,
                       dweights = df_resp$d,
                       N = N,
                       pop_quantiles = quants_known,
                       method = "linear",
                       backend = "sampling")
## estimate quantiles
y_quant_hat1 <- laeken::weightedQuantile(x = df_resp$y,
                                         probs = probs,
                                         weights = result1$g*df_resp$d)
x_quant_hat1 <- laeken::weightedQuantile(x = df_resp$x,
                                         probs = probs,
                                         weights = result1$g*df_resp$d)

## compare with known
data.frame(standard = y_quant_hat0, est=y_quant_hat1, true=y_quant_true)

## example 2: calibrate with quantiles (deciles) and totals
result2 <- joint_calib(formula_totals = ~x,
                       formula_quantiles = ~x,
                       data = df_resp,
                       dweights = df_resp$d,
                       N = N,
                       pop_quantiles = quants_known,
                       pop_totals = totals_known,
                       method = "linear",
                       backend = "sampling")
## estimate quantiles
y_quant_hat2 <- laeken::weightedQuantile(x = df_resp$y,
                                         probs = probs,
                                         weights = result2$g*df_resp$d)
x_quant_hat2 <- laeken::weightedQuantile(x = df_resp$x,
                                         probs = probs,
                                         weights = result2$g*df_resp$d)

## compare with known
data.frame(standard = y_quant_hat0, est1=y_quant_hat1,
           est2=y_quant_hat2, true=y_quant_true)

## example 3: calibrate wigh quantiles (deciles) and totals with
## hyperbolic sinus (sinh) and survey package

result3 <- joint_calib(formula_totals = ~x,
                       formula_quantiles = ~x,
                       data = df_resp,
                       dweights = df_resp$d,
                       N = N,
                       pop_quantiles = quants_known,
                       pop_totals = totals_known,
                       method = "sinh",
                       backend = "survey")

## estimate quantiles
y_quant_hat3 <- laeken::weightedQuantile(x = df_resp$y,
                                         probs = probs,
                                         weights = result3$g*df_resp$d)
x_quant_hat3 <- laeken::weightedQuantile(x = df_resp$x,
                                         probs = probs,
                                         weights = result3$g*df_resp$d)

## example 4: calibrate wigh quantiles (deciles) and totals with ebal package
result4 <- joint_calib(formula_totals = ~x,
                       formula_quantiles = ~x,
                       data = df_resp,
                       dweights = df_resp$d,
                       N = N,
                       pop_quantiles = quants_known,
                       pop_totals = totals_known,
                       method = "eb",
                       backend = "ebal")

## estimate quantiles
y_quant_hat4 <- laeken::weightedQuantile(x = df_resp$y,
                                         probs = probs,
                                         weights = result4$g*df_resp$d)
x_quant_hat4 <- laeken::weightedQuantile(x = df_resp$x,
                                         probs = probs,
                                         weights = result4$g*df_resp$d)

## compare with known
data.frame(standard = y_quant_hat0,
           est1=y_quant_hat1,
           est2=y_quant_hat2,
           est3=y_quant_hat3,
           est4=y_quant_hat4,
           true=y_quant_true)
## compare with known X
data.frame(standard = x_quant_hat0,
           est1=x_quant_hat1,
           est2=x_quant_hat2,
           est3=x_quant_hat3,
           est4=x_quant_hat4,
           true = quants_known$x)

Function to balance the covariate distributions of a control and treatment group using joint_calib

Description

joint_calib_att allows quantile or mean and quantile balancing of the covariate distributions of the control and treatment groups. It provides a user-friendly interface for specifying the variables and quantiles to be balanced. joint_calib_att uses joint_calib function, so the user can apply different methods to find the weights that balance the control and treatment groups. For more details see joint_calib() and Beręsewicz and Szymkowiak (2023) working paper.

Usage

joint_calib_att(
  formula_means = NULL,
  formula_quantiles = NULL,
  treatment = NULL,
  data,
  probs = c(0.25, 0.5, 0.75),
  ...
)

Arguments

formula_means

a formula with variables to be balanced at means,

formula_quantiles

a formula with variables to be balanced at quantiles,

treatment

a formula with a treatment indicator,

data

a data.frame with variables,

probs

a vector or a named list of quantiles to be balanced (default is c(0.25, 0.5, 0.75)),

...

other parameters passed to joint_calib function.

Value

Returns a list with containing:

  • g – g-weight that sums up to treatment group size,

  • Xs – matrix used for balancing (i.e. Intercept, X based on formula_means and X_q transformed for balancing of quantiles based on formula_quantiles and probs),

  • totals – a vector of treatment reference size (N), means (pop_totals) and order of quantiles (based on formula_quantiles and probs).

  • method – selected method,

  • backend – selected backend.

Author(s)

Maciej Beręsewicz

References

Beręsewicz, M. and Szymkowiak, M. (2023) A note on joint calibration estimators for totals and quantiles Arxiv preprint https://arxiv.org/abs/2308.13281

Greifer N (2023). WeightIt: Weighting for Covariate Balance in Observational Studies. R package version 0.14.2, https://CRAN.R-project.org/package=WeightIt.

Greifer N (2023). cobalt: Covariate Balance Tables and Plots. R package version 4.5.1, https://CRAN.R-project.org/package=cobalt.

Ho, D., Imai, K., King, G., and Stuart, E. A. (2011). MatchIt: Nonparametric Preprocessing for Parametric Causal Inference. Journal of Statistical Software, 42(8), 1–28. https://doi.org/10.18637/jss.v042.i08

Xu, Y., and Yang, E. (2023). Hierarchically Regularized Entropy Balancing. Political Analysis, 31(3), 457-464. https://doi.org/10.1017/pan.2022.12

Examples

## generate data as in the hbal package
set.seed(123)
N <- 1500
X1 <- rnorm(N)
X2 <- rnorm(N)
X3 <- rbinom(N, size = 1, prob = .5)
X1X3 <- X1*X3
D_star <- 0.5*X1 + 0.3*X2 + 0.2*X1*X2 - 0.5*X1*X3 -1
D <- ifelse(D_star > rnorm(N), 1, 0)
y <- 0.5*D + X1 + X2 + X2*X3 + rnorm(N)
dat <- data.frame(D = D, X1 = X1, X2 = X2, X3 = X3, X1X3=X1X3, Y = y)
head(dat)

## Balancing means of X1, X2 and X3 and quartiles (0.25, 0.5, 0.75) of X1 and X2
## sampling::raking is used
results <- joint_calib_att(
formula_means = ~ X1 + X2 + X3,
formula_quantiles = ~ X1 + X2,
treatment = ~ D,
data = dat,
method = "raking"
)

## Results are presented with summary statistics of balance weights (g-weights)
## and information on the accuracy of reproducing reference treatment distributions
results

## An interaction between X1 and X2 is added to means
results2 <- joint_calib_att(
formula_means = ~ X1 + X2 + X3 + X1*X3,
formula_quantiles = ~ X1 + X2,
treatment = ~ D,
data = dat,
method = "raking"
)

## Results with interaction are presented below
results2

## As noted in the documentation, the probs argument can be a named list of different orders
## In this example, we specify that X1 should be balanced at the mean,
## while X2 should be balanced at Q1 and Q3
results3 <- joint_calib_att(
formula_means = ~ X1 + X2 + X3 + X1*X3,
formula_quantiles = ~ X1 + X2,
treatment = ~ D,
data = dat,
method = "raking",
probs = list(X1 = 0.5, X2 = c(0.25, 0.75))
)

## Results with different orders are presented below
results3

## Finally, we specify an order of quantile for the interaction
results4 <- joint_calib_att(
formula_means = ~ X1 + X2 + X3,
formula_quantiles = ~ X1 + X2 + X1:X3,
treatment = ~ D,
data = dat,
probs = list(X1=0.5, X2 = c(0.25, 0.5), `X1:X3` = 0.75),
method = "raking"
)

## Results with Q3 balancing for interaction are presented below
results4

Function to balance the covariate distributions using covariate balancing propensity score CBPS

Description

joint_calib_cbps allows quantile or mean and quantile balancing of the covariate distributions of the control and treatment groups using the covariate balancing propensity score method (Imai & Ratkovic (2014)). CBPS::CBPS() and CBPS::hdCBPS() are used a backend for estimating the parameters. This function works in a similar way to the joint_calib_att() function, i.e. the user can specify variables for the balancing means as well as the quantiles.

Usage

joint_calib_cbps(
  formula_means = NULL,
  formula_quantiles = NULL,
  treatment = NULL,
  data,
  probs = c(0.25, 0.5, 0.75),
  control = control_calib(),
  standardize = FALSE,
  method = "exact",
  variable_selection = FALSE,
  target = NULL,
  ...
)

Arguments

formula_means

a formula with variables to be balanced at means,

formula_quantiles

a formula with variables to be balanced at quantiles,

treatment

a formula with a treatment indicator,

data

a data.frame with variables,

probs

a vector or a named list of quantiles to be balanced (default is c(0.25, 0.5, 0.75)),

control

a control list of parameters for creation of X_q matrix based on formula_quantiles and probs (see joint_calib_create_matrix()),

standardize

default is FALSE, which normalizes weights to sum to 1 within each treatment group (passed to CBPS() function),

method

default is "exact". Choose "over" to fit an over-identified model that combines the propensity score and covariate balancing conditions; choose "exact" to fit a model that only contains the covariate balancing conditions (passed to CBPS() function)

variable_selection

default is FALSE. Set to TRUE to select high dimension CBPS via CBPS::hdCBPS(),

target

specify target (y) variable for hdCBPS function,

...

other parameters passed to CBPS or hdCBPS functions.

Details

Imports for the function

Value

Returns a CBPS or a list object as a result of the hdCBPS function.

Author(s)

Maciej Beręsewicz

References

Imai, K., and Ratkovic, M. (2014). Covariate balancing propensity score. Journal of the Royal Statistical Society Series B: Statistical Methodology, 76(1), 243-263.

Fong C, Ratkovic M, and Imai K (2022). CBPS: Covariate Balancing Propensity Score. R package version 0.23, https://CRAN.R-project.org/package=CBPS.

Examples

## generate data as in the hbal package (see [hbal::hbal()])
set.seed(123)
N <- 1500
X1 <- rnorm(N)
X2 <- rnorm(N)
X3 <- rbinom(N, size = 1, prob = .5)
X1X3 <- X1*X3
D_star <- 0.5*X1 + 0.3*X2 + 0.2*X1*X2 - 0.5*X1*X3 - 1
D <- ifelse(D_star > rnorm(N), 1, 0) # Treatment indicator
y <- 0.5*D + X1 + X2 + X2*X3 + rnorm(N) # Outcome
dat <- data.frame(D = D, X1 = X1, X2 = X2, X3 = X3, X1X3 = X1X3, Y = y)
head(dat)

## Balancing means of X1, X2 and X3 and quartiles (0.25, 0.5, 0.75) of X1 and X2.
result <- joint_calib_cbps(formula_means = ~ X1 + X2 + X3,
                           formula_quantiles = ~ X1 + X2,
                           treatment = ~ D,
                           data = dat)

## CBPS output is presented
result

## calculate ATE by hand
w_1 <- dat$D/fitted(result)
w_1 <- w_1/mean(w_1)
w_0 <- (1-dat$D)/(1-fitted(result))
w_0 <- w_0/mean(w_0)
mean((w_1-w_0)*dat$Y)

## Compare with standard CBPS using only means
result2 <- CBPS::CBPS(D ~ X1 + X2 + X3, data = dat, method = "exact", standardize = FALSE, ATT = 0)

## calculate ATE by hand
w_1a <- dat$D/fitted(result2)
w_1a <- w_1a/mean(w_1a)
w_0a <- (1-dat$D)/(1-fitted(result2))
w_0a <- w_0a/mean(w_0a)
mean((w_1a-w_0a)*dat$Y)

An internal function to create an A matrix for calibration of quantiles

Description

joint_calib_create_matrix is function that creates an \(A = [a_{ij}]\) matrix for calibration of quantiles. Function allows to create matrix using logistic interpolation (using stats::plogis, default) or linear (as in Harms and Duchesne (2006), i.e. slightly modified Heavyside function).

In case of logistic interpolation elements of \(A\) are created as follows

\[a_{i j} = \frac{1}{(1 + \exp\left(-2l\left(x_{ij}-Q_{x_j, \alpha}\right)\right))N},\]

where \(x_{ij}\) is the \(i\)th row of the auxiliary variable \(X_j\), \(N\) is the population size, \(Q_{x_j, \alpha}\) is the known population \(\alpha\)th quantile, and \(l\) is set to -1000 (by default).

In case of linear interpolation elements of \(A\) are created as follows

\[a_{i j}= \begin{cases} N^{-1}, & x_{i j} \leqslant L_{x_{j}, r} \left(Q_{x_j, \alpha}\right), \cr N^{-1} \beta_{x_{j}, r}\left(Q_{x_j, \alpha}\right), & x_{i j}=U_{x_{j}, r}\left(Q_{x_j, \alpha}\right), \cr 0, & x_{i j}>U_{x_{j}, r} \left(Q_{x_j, \alpha}\right), \end{cases}\]

\(i=1,...,r\), \(j=1,...,k\), where \(r\) is the set of respondents, \(k\) is the auxiliary variable index and

\[L_{x_{j}, r}(t) = \max \left\lbrace\left\lbrace{x_{i j}}, i \in s \mid x_{i j} \leqslant t\right\rbrace \cup \lbrace-\infty\rbrace \right\rbrace,\] \[U_{x_{j}, r}(t) = \min \left\lbrace\left\lbrace{x_{i j}}, i \in s \mid x_{i j}>t\right\rbrace \cup \lbrace\infty\rbrace \right\rbrace,\] \[\beta_{x_{j}, r}(t) = \frac{t-L_{x_{j}, s}(t)}{U_{x_{j}, s}(t)-L_{x_{j}, s}(t)},\]

\(i=1,...,r\), \(j=1,...,k\), \(t \in \mathbb{R}\).

Usage

joint_calib_create_matrix(X_q, N, pop_quantiles, control = control_calib())

Arguments

X_q

matrix of variables for calibration of quantiles,

N

population size for calibration of quantiles,

pop_quantiles

a vector of population quantiles for X_q,

control

a control parameter for creation of X_q matrix.

Value

Return matrix A

Author(s)

Maciej Beręsewicz

References

Harms, T. and Duchesne, P. (2006). On calibration estimation for quantiles. Survey Methodology, 32(1), 37.

Examples

# Create matrix for one variable and 3 quantiles
set.seed(123)
N <- 1000
x <- as.matrix(rnorm(N))
quants <- list(quantile(x, c(0.25,0.5,0.75)))
A <- joint_calib_create_matrix(x, N, quants)
head(A)
colSums(A)

# Create matrix with linear interpolation
A <- joint_calib_create_matrix(x, N, quants, control_calib(interpolation="linear"))
head(A)
colSums(A)

# Create matrix for two variables and different number of quantiles

set.seed(123)
x1 <- rnorm(N)
x2 <- rchisq(N, 1)
x <- cbind(x1, x2)
quants <- list(quantile(x1, 0.5), quantile(x2, c(0.1, 0.75, 0.9)))
B <- joint_calib_create_matrix(x, N, quants)
head(B)
colSums(B)