Liner regression between 2 variables but only in selected lines.

[andresrcs]

Take a look at this related thread, this shows how to perform linear regressions over nested subgroups of your data frame

Linear regression by rows

You can use this example as starting point library(dplyr) library(tidyr) library(purrr) library(broom) data <- data.frame(stringsAsFactors=FALSE, ITEM = c("item A", "item B"), JAN = c(10, 30), FEB = c(20, 35), MAR = c(15, 37), APR = c(17, 38) ) fit_model <- function(df) lm(value ~ n, data = df) get_slope <- function(mod) tidy(mod)$estimate[2] data %>% gather('month', 'value', -ITEM) %>% group_by(ITEM) %>% mutate(n = row_number()) %>% arrange(ITEM, n) %>% nest() %>% mutate(model = map(data, fit_model)) %>% mutate(slope = map_dbl(model, get_sl…

If you need more specific help, please provide a proper REPRoducible EXample (reprex) illustrating your issue.