diff --git a/DESCRIPTION b/DESCRIPTION
index 1e12a4f9..d24b93e0 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -1,7 +1,7 @@
 Package: TwoSampleMR
 Title: Two Sample MR Functions and Interface to MRC Integrative
     Epidemiology Unit OpenGWAS Database
-Version: 0.7.2
+Version: 0.7.3
 Authors@R: c(
     person("Gibran", "Hemani", , "g.hemani@bristol.ac.uk", role = c("aut", "cre"),
            comment = c(ORCID = "0000-0003-0920-1055")),
diff --git a/NEWS.md b/NEWS.md
index fb6fda5a..167424f3 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -1,3 +1,9 @@
+# TwoSampleMR v0.7.3
+
+(Release date 2026-03-31)
+
+* Some further code optimizations.
+
 # TwoSampleMR v0.7.2
 
 (Release date 2026-03-30)
diff --git a/R/format_mr_results2.R b/R/format_mr_results2.R
index 6be97cfe..4c6e73c2 100644
--- a/R/format_mr_results2.R
+++ b/R/format_mr_results2.R
@@ -146,9 +146,13 @@ combine_all_mrresults <- function(
   het <- het[, c("id.exposure", "id.outcome", "method", "Q", "Q_df", "Q_pval")]
 
   # Convert all factors to character
-  res[] <- lapply(res, function(x) if (is.factor(x)) as.character(x) else x)
-  het[] <- lapply(het, function(x) if (is.factor(x)) as.character(x) else x)
-  sin[] <- lapply(sin, function(x) if (is.factor(x)) as.character(x) else x)
+  factors_to_character <- function(df) {
+    df[] <- lapply(df, function(x) if (is.factor(x)) as.character(x) else x)
+    df
+  }
+  res <- factors_to_character(res)
+  het <- factors_to_character(het)
+  sin <- factors_to_character(sin)
 
   sin <- sin[grep("[:0-9:]", sin$SNP), ]
   sin$method <- "Wald ratio"
@@ -285,10 +289,10 @@ combine_all_mrresults <- function(
 power_prune <- function(dat, method = 1, dist.outcome = "binary") {
   # dat[,c("eaf.exposure","beta.exposure","se.exposure","samplesize.outcome","ncase.outcome","ncontrol.outcome")]
   if (method == 1) {
-    L <- NULL
     id.sets <- paste(split_exposure(dat)$exposure, split_outcome(dat)$outcome)
     id.set.unique <- unique(id.sets)
     dat$id.set <- as.numeric(factor(id.sets))
+    L <- vector("list", length(id.set.unique))
     for (i in seq_along(id.set.unique)) {
       # print(i)
       print(paste(
@@ -334,7 +338,7 @@ power_prune <- function(dat, method = 1, dist.outcome = "binary") {
       dat1 <- dat1[nexp == nexp[1], ]
       L[[i]] <- dat1
     }
-    dat <- do.call(rbind, L)
+    dat <- data.table::rbindlist(L)
     dat <- dat[, !names(dat1) %in% c("id.set", "id.subset")]
     # if (drop.duplicates == T) {
     # 	dat<-dat[dat$power.prune=="keep",]
@@ -343,17 +347,17 @@ power_prune <- function(dat, method = 1, dist.outcome = "binary") {
   }
 
   if (method == 2) {
-    L <- NULL
     id.sets <- paste(split_exposure(dat)$exposure, split_outcome(dat)$outcome)
     id.set.unique <- unique(id.sets)
     dat$id.set <- as.numeric(factor(id.sets))
+    L <- vector("list", length(id.set.unique))
     for (i in seq_along(id.set.unique)) {
       dat1 <- dat[id.sets == id.set.unique[i], ]
       # unique(dat1[,c("exposure","outcome")])
       id.subset <- paste(dat1$exposure, dat1$id.exposure, dat1$outcome, dat1$id.outcome)
       id.subset.unique <- unique(id.subset)
       dat1$id.subset <- as.numeric(factor(id.subset))
-      L1 <- NULL
+      L1 <- vector("list", length(id.subset.unique))
       for (j in seq_along(id.subset.unique)) {
         # print(j)
         print(paste("identifying best powered summary set: ", id.subset.unique[j], sep = ""))
@@ -405,12 +409,12 @@ power_prune <- function(dat, method = 1, dist.outcome = "binary") {
         # dat2$power<-power
         L1[[j]] <- dat2
       }
-      L[[i]] <- do.call(rbind, L1)
+      L[[i]] <- data.table::rbindlist(L1)
     }
-    dat2 <- do.call(rbind, L)
+    dat2 <- data.table::rbindlist(L)
     dat2 <- dat2[order(dat2$id.set, dat2$iv.se), ]
     id.sets <- unique(dat2$id.set)
-    id.keep <- NULL
+    id.keep <- vector("list", length(id.sets))
     for (i in seq_along(id.sets)) {
       # print(i)
       # print(id.sets[i])
@@ -450,6 +454,6 @@ size.prune <- function(dat) {
   dat$ncase[is.na(dat$ncase)] <- dat$samplesize[is.na(dat$ncase)]
   dat <- dat[order(dat$ncase, decreasing = TRUE), ]
   id.expout <- paste(dat$exposure, dat$outcome)
-  id.keep <- id.expout[!duplicated(paste(dat$exposure, dat$originalname.outcome))]
+  id.keep <- id.expout[!duplicated(data.frame(dat$exposure, dat$originalname.outcome))]
   dat <- dat[id.expout %in% id.keep, ]
 }
diff --git a/R/harmonise.R b/R/harmonise.R
index 54e9a253..75436d3f 100644
--- a/R/harmonise.R
+++ b/R/harmonise.R
@@ -70,7 +70,7 @@ harmonise_data <- function(exposure_dat, outcome_dat, action = 2) {
 
   combs <- subset(
     res.tab,
-    !duplicated(paste(id.exposure, id.outcome)),
+    !duplicated(data.frame(id.exposure, id.outcome)),
     select = c(id.exposure, id.outcome)
   )
 
diff --git a/R/other_formats.R b/R/other_formats.R
index cee95686..ab48b67c 100644
--- a/R/other_formats.R
+++ b/R/other_formats.R
@@ -146,7 +146,7 @@ run_mr_presso <- function(dat, NbDistribution = 1000, SignifThreshold = 0.05) {
   dat <- subset(dat, mr_keep)
   d <- subset(
     dat,
-    !duplicated(paste(id.exposure, " - ", id.outcome)),
+    !duplicated(data.frame(id.exposure, id.outcome)),
     select = c(exposure, outcome, id.exposure, id.outcome)
   )
   res <- list()
diff --git a/R/rucker.R b/R/rucker.R
index 5660c7e3..c207abfe 100644
--- a/R/rucker.R
+++ b/R/rucker.R
@@ -30,10 +30,10 @@ PM <- function(y = y, s = s, Alpha = 0.1) {
   mode <- df - 1
   Quant <- c(low, mode, mn, med, up)
   L <- length(Quant)
-  Tausq <- NULL
-  Isq <- NULL
+  Tausq <- numeric(L)
+  Isq <- numeric(L)
   CI <- matrix(nrow = L, ncol = 2)
-  MU <- NULL
+  MU <- numeric(L)
   v <- 1 / s^2
   sum.v <- sum(v)
   typS <- sum(v * (k - 1)) / (sum.v^2 - sum(v^2))
@@ -77,7 +77,7 @@ mr_rucker <- function(dat, parameters = default_parameters()) {
   dat <- subset(dat, mr_keep)
   d <- subset(
     dat,
-    !duplicated(paste(id.exposure, " - ", id.outcome)),
+    !duplicated(data.frame(id.exposure, id.outcome)),
     select = c(exposure, outcome, id.exposure, id.outcome)
   )
   res <- list()
@@ -409,7 +409,7 @@ mr_rucker_jackknife <- function(dat, parameters = default_parameters()) {
   dat <- subset(dat, mr_keep)
   d <- subset(
     dat,
-    !duplicated(paste(id.exposure, " - ", id.outcome)),
+    !duplicated(data.frame(id.exposure, id.outcome)),
     select = c(exposure, outcome, id.exposure, id.outcome)
   )
   res <- list()